1. Field of the Invention
The present invention relates to a novel planographic printing plate precursor. In particular, the invention relates to a novel planographic printing plate precursor that is scanning-exposed to laser light on the basis of digital signals, has excellent sensitivity and resistance to stains, and with which easy in-printer development is made possible. The present invention also relates to a novel surface hydrophilic material and a substrate used for a planographic printing plate precursor which are excellent in hydrophilicity and durability
2. Description of the Related Art
Planographic printing utilizes plate material including an ink-receiving lipophilic region and an ink-repellent region (hydrophilic region) that receives dampening water without receiving ink, and photosensitive planographic printing plate precursors (PS plates) are currently being widely used.
PS plates typically comprise a support, such as an aluminum plate, having disposed thereon a photosensitive layer. The PS plate is exposed imagewise and developed, whereby the photosensitive layer in a non-image area is removed, and printing is conducted utilizing hydrophilicity of the support surface and hydrophobicity of the photosensitive layer in an image area. It is necessary for the support surface to be highly hydrophilic in order to prevent the non-image area from being stained.
Conventionally, anodized aluminum plates or anodized aluminum plates which is subjected to silicate treatment in order to raise hydrophilicity have been used for the hydrophilic support or a hydrophilic layer. Much research relating to hydrophilized substrate and hydrophilic layers using such aluminum supports is being conducted. For example, Japanese Patent Application Laid-open (JP-A) No. 7-1853 discloses a support processed with an undercoating agent of polyvinylphosphonic acid, and JP-A No. 59-101651 discloses using a polymer including a sulfonic acid group as an undercoat layer underlying a photosensitive layer. In addition, there have also been proposals to use polyvinylbenzoic acid and the like as an undercoat agent.
There have been many proposals with respect to hydrophilic layers when flexible supports comprising PET (polyethylene terephthalate) or cellulose triacetate rather than using a metal support such as aluminum are used. For example, JP-A No. 8-292558 discloses a swelling hydrophilic layer comprising a hydrophilic polymer and a hydrophobic polymer, EP No. 0709228 discloses a PET support including a microporous, hydrophilic crosslinked silicate surface, and JP-A Nos. 8-272087 and 8-507727 disclose a hydrophilic layer that contains a hydrophilic polymer and is cured with hydrolyzed tetraalkyl orthosilicate.
These hydrophilic layers are more hydrophilic than conventional ones, and provide planographic printing plates with which stainless prints can be obtained when printing is initiated. However, there are problems in that the layers peel during the course of repeated printing and their hydrophilicity drops over time. There is thus a demand for planographic printing plate precursors with which many stainless prints can be obtained without the hydrophilic layer peeling from the support and without surface hydrophilicity dropping, even in severe printing conditions. There is also a demand for improved hydrophilicity from a practical perspective.
Numerous studies have been conducted in regard to printing plates for computer-to-plate systems, the development of which has been remarkable in recent years. Development-less planographic printing plate precursors that can be set in a printer to print without being developed after exposure are being researched with the aim of boosting process rationalization and solving the problem of waste treatment, and various methods have been proposed.
Namely, there has been the desire to simplify or eliminate altogether having to dissolve and remove the non-image area with an alkali developing solution (additional wet processing), which is customary in conventional processes for producing planographic printing plates. Particularly in recent years, because disposal of waste solution generated by wet processing is becoming a great concern in the entire industry in view of the global environment, the demand for improvement continues to grow ever stronger.
In response to this demand, there has been proposed a method using a printing plate precursor disposed with a thermosensitive recording layer, in which the non-image area is removable during the course of ordinary printing. After being exposed, the printing plate precursor is developed in a printer to obtain a final printing plate. Specifically, the exposed printing plate precursor is mounted on a cylinder in the printer without having been developed by a developer, and the non-image area of the planographic printing plate precursor is removed with ink and/or dampening water supplied thereto while the cylinder is rotated. This is referred to as in-printer development.
Planographic printing plate precursors suited to in-printer development must have a photosensitive layer that is soluble in dampening water or in an ink solvent, and they must be suitable for development in a printer set in a luminous room.
WO 94/23954 discloses a printing plate comprising a support having disposed thereon a crosslinked hydrophilic layer containing microcapsules of a thermo-fuseable substance. The microcapsules are broken by the action of heat generated in the region exposed to a laser light, and a lipophilic substance dissolves out of the broken microcapsules to thereby hydrophobicate the surface of the hydrophilic layer. Although the printing plate precursor does not require development, there is a problem in that the hydrophilicity and durability of the hydrophilic layer disposed on the support are unsatisfactory, and stains gradually appear in the non-image area in the course of printing.
One promising example relating to a thermosensitive recording layer having excellent in-printer developability is a thermosensitive planographic printing plate precursor that includes, as a thermosensitive image forming layer, a hydrophilic layer that contains hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder polymer. This printing plate precursor utilizes the principle that, when heat is applied to the thermosensitive layer, the hydrophobic thermoplastic polymer particles fuse, and the surface of the hydrophilic thermosensitive layer changes into a lipophilic image area.
However, while such planographic printing plate precursors exhibit good in-printer developability, there is a problem in that thermal energy is not sufficiently used in the image forming reaction due to the generated heat being diffused into the aluminum support in the precursor, and sensitivity is therefore low. Another problem is that, when fusion of the particles is insufficient, the image area of the thermosensitive layer becomes weak and printing durability becomes insufficient.
As a countermeasure, JP-A No. 2001-213062 proposes disposing an insulation layer comprising a water-insoluble organic polymer between the aluminum support and the thermosensitive layer. With this insulation layer, it has become possible to improve sensitivity without lowering printing durability. However, with regard to hydrophilicity of the support surface, there is still room for improvement in view of maintaining high hydrophilicity wherein stains do not appear in the non-image area over a long period of time.
On the other hand, resin films have been used for various purposes, and surfaces thereof have hydrophobic property in general. Almost inorganic materials such as glass and metal also have hydrophobic property. If surfaces of the films and materials have hydrophilicity, water droplets can adhere thereto, spread uniformly and forms water-film thereon. Therefore, cloud or mist can be prevented. Further, due to the hydrophilicity, unpreferable hydrophobic contaminants such as sealant, grease and combustion product such as carbon black, which are comprised in municipal soot, automotive exhaust gas and the like, are hard to adhere to the film and the like. Even if the hydrophobic contaminants adhere to the film and the like, it is easy to remove the hydrophobic contaminants by washing it or rain. As a method for providing hydrophilic property to a surface of the materials, etching method and plasma method have been proposed, and these methods can provide excellent hydrophilicity thereto. However, the effects thereof can not be maintained. Further, a surface hydrophilic coating film comprising hydrophilic polymer is also proposed (Dairy Chemical Industry News Paper, Jan. 30, 1995). However, when the coating film is provided on a substrate, an affinity of the coating film and the substrate is insufficient. Furthermore, a film wherein titanium oxide is used is known. For example, a layer comprising a photocatalyst is disclosed in PCT/JP96/00733. The layer is provided on a substrate, and the surface thereof has excellent hydrophilicity in accordance with an optical excitation due to photocatalyst. However, a hydrophilic film comprising the titanium oxide has insufficient film strength.